Since the 1970's there has been a great need to use rapidly moving doors in buildings for industrial use. This applies to openings indoors as well as in external walls, where the door provides shielding between different activities or prevents drafts and heat losses. Presently, rolling doors with flexible door leaves are used for this purpose, but also more rigid constructions like slatted doors with polymeric or metallic lamellae are used. These doors are rolled up on an overhead drive cylinder and can be provided with additional elements like transverse wind reinforcements on the door leaf to counteract wind load, a weight balance system, tensioning system, windows or the like. For safety reasons, rolling doors can be further provided with safety edge protection, failsafe devices, drop protection, and crash safety functions.
U.S. Pat. No. 5,222,541 teaches a roll-up industrial door with a counter-balancing and tensioning system which counter-balances the weight of the door panel and, through a biasing mechanism, applies a downward tension to the closed door panel to stretch the panel and resist wind deflection. It is noted that the system operates with constant force in the pull-down direction, but contains no locking of the door leaf in the lower position. In any case, the invention is primarily directed to a break-away function.
U.S. Pat. No. 5,474,117 describes a locking mechanism for a roll-up closure with horizontal slats. The lowermost and uppermost slats carry spring-biased pins which resist unintentional lifting of the closure. The drawings of this patent shows a door locked at the bottom. It is noted that similar solutions have been previously proposed, but mainly as catching devices.
A related door construction is disclosed in U.S. Pat. No. 5,632,317. The invention is a roll-up door assembly with a number of embodiments including a moveable barrier bar to minimize deflection of the door closure member, or curtain, due to wind or other pressure generating forces. However, this solution is very complex and contains expensive elements. In addition, manual locking of the door is also provided for added wind resistance.
U.S. Pat. No. 6,439,292 is a roll-up door with a crash safety system that can automatically return the door to an operational condition. In the event that the door is not automatically restored to operation, it can be restored manually. It is noted that this patent presents a break-away function in combination with a photocell for safe operation during opening and closing of the door.
While some of the foregoing references have certain attendant advantages, further improvements and/or alternative forms, are always desirable.